脉冲CO2激光高精度烧蚀熔石英玻璃

High precision laser ablation of fused silica using pulsed CO2 laser

激光抛光是一种能获得超光滑表面新颖的光学元件加工方法,但抛光后表面存在残余波纹和面形畸变.激光高精度烧蚀可用于对元件表面残余波纹和面形进行修正,是一种极具潜力的修形技术.本文开展了激光高精度烧蚀熔石英玻璃的实验,验证了脉冲CO2激光通过控制重叠率可以实现高精度的局部区域均匀烧蚀,并可通过控制激光功率密度获得不同纳米量级的烧蚀深度.但实验发现激光局部区域烧蚀过程存在热累积和过烧蚀的现象.为此建立三维数值模型模拟脉冲CO2激光扫描熔石英表面的过程,对不同重叠率及不同脉冲重复频率作用下熔石英表面温度分布及演变进行分析.数值计算结果表明,重叠率过高将导致熔石英过烧蚀;在合适的重叠率下,高脉冲重复频率会导致明显的热累积.

Laser polishing is a novel processing method which can achieve a super-smooth surface of an optical component.However,there are residual ripples and surface distortions after laser polishing.High precision laser ablation can be used to correct the residual ripple and shape of the component,making it a promising figuring method.In this paper,the experiment of high precision laser ablation of fused silica was carried out with pulsed CO2 laser.It is verified that highprecision uniform ablation in a local region can be achieved by controlling the laser overlap rate,and different nanometer ablation depths can be obtained by controlling the laser power density.However,it has been found that there is thermal accumulation and over-ablation during the laser ablation process.A three-dimensional numerical model was established to simulate the process of pulsed CO2 laser scanning on a fused silica surface.The surface temperature distribution and evolution of fused silica with different overlap rates and pulse repetition frequencies were analyzed.The numerical results show that the increase of the overlap rate could lead to over-ablation.With a suitable overlap rate,the high pulse repetition frequency could result in significant heat accumulation.